The present disclosure relates generally to industrial automation and control systems, such as those used in industrial and commercial settings. More particularly, the present disclosure relates to high reliability or safety industrial controllers appropriate for use in devices intended to protect human life and health.
Industrial controllers are special purpose computers used in controlling industrial processes. Under the direction of a stored, controlled program, an industrial controller examines a series of inputs reflecting the status of the controlled process and changes a series of outputs controlling the industrial process. The inputs and outputs may be binary, i.e. on or off or analog, providing a value within a substantially continuous range. The inputs may be obtained from sensors attached to the controlled process and the outputs may be provided to actuators on the controlled process.
Safety systems are systems intended to ensure the safety of humans working in the environment of an industrial process. Such systems may include the electronics associated with emergency stop buttons, light curtains and other machine lockouts. Traditionally, safety systems have been implemented by a set of redundant circuits separate from the industrial control system used to control the industrial process with which the safety system is associated. Such safety systems have been hardwired from switches and relays, including specialized safety relays which provide comparison of redundant signals and internal checking of all conditions, such as welded or stuck contacts.
Safety control can be implemented in various manners, depending on the required control complexity and safety complexity, which takes into account the number of controlled zones. A safety controller can be provided in the form of a safety relay for local, small-scale and/or simple safety control, as a module for a modular, more complex configuration or as a more sophisticated but still compact programmable logic controller, fulfilling certain safety ratings. A compact safety controller can be employed within a complex safety network. Safety relays, on the other hand, are particularly useful for small scale emergency stop applications.
A safety device oftentimes is configured to comply with standardized requirements, like a safety integrity level (SIL). Traditional safety control devices are not expandable. Accordingly, the input and output terminals are limited to the originally provided ones of the safety control device, thus limiting the range of applications and generating a need for increased wiring between safety control devices and/or standard control devices.
This is particularly disadvantageous where the safety controller resides within a small cabinet or enclosure where space is limited. Further, increased wiring between components is not desirable in hazardous environments or rough working environments. Conventional expansion of existing safety control systems required I/O to be added in the vicinity of the safety controller, for instance in a side-by-side relation, and cable wiring between the safety controller or small scale safety relay and an I/O device. However, this expanse of the footprint of the controller and the additional wiring or added cable between the safety controller and the I/O component makes the system susceptible to failure, in particular in hazardous or rough environments. Also, such conventional safety controllers either remain restricted to proprietary safety functions or, where making use of the additional I/O, may jeopardize safety.
It is therefore desirable to provide an improved safety controller and industrial control system as well as method that overcomes the above disadvantages in the prior art.